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ABSTRACT
Electric power distribution is the most valuable part of electrical power system in the process of
delivering electricity to consumer. Electric power companies are now-a-days adopting some
advanced systems such as computer aided monitoring control and management of electric power,
so that it can provide better services to electric consumers. This project results an approach to
automate the electricity billing system. The concept of prepaid is one of the emerging fields for
the paid service providers. The concept is becoming so popular because it has so many
advantages. The services like electricity, gas, water telephone etc are now days get privatized.
The service provider company some time incurs heavy losses due to non collection of bills.
These service items cannot be recovered from the user after providing, so the concept of prepaid
reduce risk and increase profitability. Also the bill collection infrastructure is not necessary
which intern increase improve the efficiency of the service providing companies. The concept of
prepaid starts in the manual form by receiving advance deposits but now due to the revolution of
IT and electronics industry the manual recharging process is replaced with automatic and
electronic recharging. The recharging methods can be with wire based like telephone line and
also by using wireless technology like radio and bluetooth communication. The prepaid system is
designed with a smart technology using microcontroller and the recharging process is by some
method of communication. The Mobile based recharging is very attractive recharging system.
The recharging can be done from any remote place without accessing the energy meter
physically. This concept of remote charging makes the system more flexible.
INTRODUCTION
Introduction
The trend of the time has always been in favour of that technology which finally become costeffective
as well as an elegant one. Traditional meter reading is done by the human operator, this
require a more number of labour operator and long working hour to achieve the complete area
data reading and billing. Due to the increase in the development of residential building and
commercial building the meter reading task increases which require more number of human
operator. In order to achieve efficient meter reading, reduce billing error and operation cost,
automatic meter reading system play an important role. Electric energy meters is the direct
billing interface between utility grid and consumers and it undergone several advancements in
the last decade.
In postpaid system, there is no control use of electricity from the consumer’s side. There is a lot
of wastage of power in the consumer’s side due to lack of planning of electrical consumption in
an efficient way.
A Prepaid Energy Meter is used to collect the electricity bills from the consumers according to
their consumption. The prepaid meter is not only limited to automate the meter reading(AMR)
but also attributed with prepaid recharging ability and information of consumed data can be
exchange between the grid and consumer .The detail of consumed data which is send by the
prepaid energy meter can be stored in the grid computer for future verification.
To automate the system of billing of energy is the main theme of this project. The front end of
this project is user friendly and the employees can work on with minimum knowledge of
computers.
2. DESIGN PRINCIPLE
The Prepaid Energy meter with Mobile Based Recharging System is designed by using a 8 bit
microcontroller. The Microcontroller receives the pulse by interfacing optical pickups from a
traditional electromagnetic energy meter. The Prepaid Energy meter with Mobile Based
Recharging System works with the principle as follows
2.1 Pulse Counting
The electronic energy meter is interfaced to the microcontroller through opto-isolator. The
energy meter receives its Input from two number of CT's, one is connected to the phase and the
other one is connected to the neutral. A V.T. through bridge rectifier is used to provide
(+5V/+12V) to the microcontroller & other component for their use. So the processor reads V
from V.T., I(depends on Power Factor) from C.T. and their product is seen on the digital screen
of the Meter. The energy meter internal circuit working with a low voltage (+5v) which is not
isolated. There are four LED on Energy Meter.
1. Phase (Mains ON)
2. Earth
3. Rev (Revolution)
4. Cal (Pulse counter)
The Microcontroller receives the pulse by interfacing optical pickups from a traditional
electromagnetic energy meter. Since the energy meter is working with a non-isolated supply, we
are using an isolation circuit to get a pulse from the energy meter called Opto-isolator circuit
using a mct2e IC.
2.2 Overload Detection
This over current relay will work for A.C. Voltage and current. The sampling method in this
design is based on the transformer principal. The load current passes through the primary of the
transformer; the drop across the transformer is very negligible as the resistance of primary circuit
is very less. But the flux developed due to primary current will induce an alternating voltage in secondary winding. That voltage is very small and also very much weak by strength. The signal
developed at the secondary is very much linear with input current until the core saturation takes
place. The transformer o/p is a proportional signal with respect to line current. As this signal is
very weak we use a buffer amplifier which is a unity gain amplifier, which doesn’t change the
value of the signal, but it increases the current or driving strength. Now this signal is sufficiently
strong to be feed in to an amplifier which is an inverting amplifier which provide a fixed gain to
the signal, the output of the amplifier is an alternating signal, which is filter rectified with a half
weave rectifier and smoothen with a filter circuit. The rectifier output signal has to be
companied with the set values. The existing comparator circuit has four comparator. So four
reference values can be set with the help of presets. The comparator is always in line with the
signal and indicates the level of current in the load line. With the help of a miniature rotary
switch one of the comparator output will be chosen. The setting of that comparator reference
voltage will be the indicative of tripping current.
2.3 Mobile Phone based recharging
In this project the Prepaid Energy meter can be charged from a remote by using a mobile. Once
the user feel to recharge the prepaid energy meter, he can transfer the amount to the service
provider bank account and the service provider will make a call to the system and log in to that
and charge it by entering digits from its key pad. The recharging can be done from any mobile
set but the system access code must be put in to the system to log into the energy meter. This
type of systems are now days getting popular. Many popular and well known companies make
products and sale in the market.
The energy meter sends a pulse to the microcontroller indicating a unit is consumed. The
controller calculate the number of pulse and display the balance units left in the system. When
the system do not have any balance it trips the main relay to disconnect the supply from load.
When the user transfer money to the service provider’s account then the service provider rings
up to the mobile connected to the system and sends a code through the DTMF coding system,
the controller programmed in the system reads that and recharge the system to start again. The
system is installed with an embedded operating system to provide a user friendly environment
with the help of alphanumeric LCD.
3. Circuit Description
3.1 Power Supply
3.1.1 Circuit Connection
Here we are using Transformer (0-12) v, 1Amp, IC 7805 and 7812, diodes IN 4007, LED and
resistors. Here 230V, 50 Hz ac signal is fed to the primary of the transformer as input and the
secondary of the transformer is fed for DC output to the bridge rectifier. The IC regulator (7805
and 7812) is fed from the output of the diode for input purpose through capacitor
(1000mf/35volt). The output of the IC regulator is given to the LED through resistors to detect
whether the supply is ON/OFF.
3.1.2 Circuit Explanations
When we give an AC signal to the primary coil of the transformer, due to the magnetic effect of
these conductors magnetic flux is induced in these conductors(primary) and this flux is
transferred to the secondary conductors by the transformer action. Transformer is an
electromechanical static device which transformer electrical energy from one conductors to
another without any change in its frequency. Here the diodes are connected in a bridge section.
The secondary conductors of the transformer is given to the bridge circuit for the purpose of
rectification.
During the positive cycle of the ac signal, the diodes D2 and D4 conduct as these diodes are
forward biased and diodes D1 and D3 does not conduct as these diodes are reverse biased.
Similarly during the negative cycle of the ac signal, the diodes D1 and D3 conduct as these
diodes are forward biased and the diodes D2 and D4 does not conduct as these diodes are reverse
biased . The output of the bridge rectifier through (D2&D4) is not a pure dc and there is rippled
ac present in it. A capacitor is jointed to the o/p of the diodes (D2&D3) to overcome that effect.
This process removes any unwanted ac signal present in it and thus we get a pure dc signal from
it. Here we need a fixed DC voltage, for that we are using IC regulators (7805 & 7812).Voltage
regulation ICs are used here to supply a constant voltage regardless of changes in load current.
These IC’s can provide fixed voltage and with adequate heat sink. The output of the bridge
rectifier is given as input to the integrated circuit regulator through a capacitor with respect to
B.Tech Project Report 2012
Dept. of Electrical Engineering Page 8
N.I.T. ROURKELA
ground and thus a fixed output is obtained. The output of the IC regulator (7805 & 7812) is given
to the LED for indication purpose through resistor that power supply is ON/OFF.LED glows ON
state due to the forward bias of the LED, and the o/p are obtained from the pin no-3
3.2 Motherboard
The motherboard of this project is made with a MSC–51 core compatible
microcontroller(AT89C51).With the help of printed circuit board, we have made the
motherboard, compatible for the microcontroller. This board is consisting of
microcontroller(AT89C51), i/p or o/p pull-up registers, oscillator section and auto reset circuit.
3.2.1 Microcontroller
The Atmel AT89 series is one of the most popular Microcontroller in use today due to their
industry standard instruction set & low unit cost .The 89C51 has three very general types of
memory. To effectively program the 89C51 it is necessary to have a basic understanding of these
memory types. They are: On-Chip Memory, External Code Memory, and External RAM. Onchip
memory refers to any memory (Code, RAM, or other) that physically exists on the
Microcontroller itself[5]. AT89C51 has 4KB Flash programmable and erasable read only
memory (PEROM).
On-Chip Memory refers to any memory (Code, RAM, or other) that physically exists on the
Microcontroller itself. On-chip memory can be of several types, but we'll get into that shortly.
External Code Memory is code (or program) memory that resides off-chip. This is often in the
form of an external EPROM.
External RAM is RAM memory that resides off-chip. This is often in the form of standard static
RAM or flash RAM.
AT89C51 has a bank of 128 bytes of Internal RAM. This Internal RAM is found on-chip so it is
the fastest RAM available, and it is also the most flexible in terms of reading, writing, and
modifying it's contents. Internal RAM is volatile, so when the 89C51 is reset this memory is
cleared[5].
3.2.2 Auto reset circuit
Pin -9 is the RESET pin. It is an input and is active high (normally low).Upon applying a high
pulse to this pin, the microcontroller will reset and terminate all activities. This is often referred
to as a power on reset. Activating a power on reset will cause all values in the register to be lost.
Figure 3.2.2 shows the power on reset circuit. In order for the RESET input to be effective, it
must have a minimum duration of two m/c cycle before it is allowed to go low. When power is
turned ON, the circuit hold the reset pin high for an amount of time that depend upon capacitor
value & the rate at which it charges. That’s why a 8.2kΩ resistor & 10μf capacitor is used
here[4].